Manure characteristics

What you need to know

Animal manures are a valuable source of nutrients for crop growth. But, since every farm operation is different, each manure will have unique characteristics. Make regular laboratory manure analysis an important step in your manure and nutrient management planning. Understand that the total nutrient content in manure is not available the first year and that some nutrients may be lost depending on management practices.

Nutrient content

Figure 1. Range of nutrient contents in different types of manures analyzed between 2012 and 2017. Manures followed by “S” are solid while manures followed by “L” are liquid.

Nutrients in manure are valuable resources, but not all manures are created equal. Manure nutrient content depends on many factors, including:

Animal species

Livestock diet

Livestock housing and bedding

Manure storage and handling system

Dilution from water (wash water or rain water)

Since these factors are different on each farm, the most reliable way to determine the nutrient content of manure is to collect a thorough sample and send

it to a laboratory for analysis. Some people may use what we call “book values” (averages published by various organizations) to estimate the nutrient content in their manure, but we do not recommend this practice. For an example see Figure 1, which shows the range of nutrient content in select manure types. Small differences between the actual nutrient content of manure and the average “book value” can cause significant over- or under-application of nutrients that may affect crop yields and water quality. For tips on collecting a thorough manure sample, see Table 1.

Liquid and semi-solid manure

The best and safest time to sample liquid manure is after the pit or lagoon has been agitated and is being pumped out.

Collect 15 to 25 samples as the pit is pumped out from beginning to end. Dump into a 5-gallon bucket.

Mix the manure thoroughly.

Take a subsample, usually about a quart, and place in a plastic container.

Freeze the sample prior to sending to the lab.

Note: This method will not allow you to get the analysis results back prior to application for the current year. However, the analysis can be used to determine whether appropriate amounts of manure were applied to meet crop needs and for estimating the Year 2 and 3 nutrient credits.

Solid manure

Manure can be sampled from the stockpile or during hauling.

Stockpile:

Using a pitchfork or shovel, collect 15 to 25 samples from many different depths in the pile but avoid the crust.

During hauling:

Collect several subsamples from each load.

Place samples into a 5-gallon bucket and mix very well.

Take a subsample and place in a sealable plastic bag, then double up the bag.

Note: With the stockpile method, you may be able to have your manure analyzed prior to application. If sampling during hauling, you will not get the analysis results back prior to application for the current year.

Nutrient Availability

Nutrients are not entirely available for crop use the first year after application. This is because nutrients can change forms, and only some of these forms are available for plants to use. When nutrients are bound to carbon they are in an organic form. If not bound to carbon, they are in an inorganic form. Typically, plants can only use the inorganic form of nutrients, but manure supplies both organic and inorganic forms. Microbes can break down organic forms of nutrients and mineralize them into inorganic forms. However, this can take several years and depends on soil moisture and temperature conditions (see Figure 2).

Figure 2. A basic outline of nutrient cycling. Manure provides both organic and inorganic forms of nutrients, but plants can typically only use inorganic forms.

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Nitrogen (N) availability in manure is more challenging to estimate than phosphorus (P) or potassium (K). “Plant Available N” (PAN) is the amount of N available from manure. We can determine this on a yearly basis. “Nitrogen credits” or “N credits” are the second and third year PAN, multiplied by the application rate. Use these N credits when planning fertilizer or manure applications in the second and third year after manure application. Typically, additional N is not released beyond three years.

Raw manure supplies two forms of N to the soil: organic-N and ammonium, an inorganic form. Ammonium is immediately available to plants, while organic-N needs to mineralize into ammonium to be useful. Ammonium can easily convert to ammonia gas in a process called volatilization, and be lost to the atmosphere if not incorporated into the soil. A third form, nitrate is also inorganic and immediately available to plants. It may be present but is usually negligible in raw manures. The overall availability of the combined forms of N depends on two main factors:

Animal species – different types of animals will have different proportions of organic-N and ammonium in their manure. For example, swine manure has a higher proportion of ammonium while dairy manure has a higher proportion of organic-N.

Manure application method – injecting liquid manures is the preferred method to minimize ammonia gas losses. When broadcasting either liquid or solid manure, incorporate them as soon as possible to reduce gas losses.

See Table 2 for the percent of total N available per year and how animal type and method of application affects it.

To calculate PAN, multiply the Total N value from the manure analysis by the N availability factor (percent total N available) for each specified year from Table 2 (see Figure 3). To determine N credits for years 2 and 3, calculate the PAN for those years and multiply by the application rate. Remember to account for N credits in those years.

Table 2. Nitrogen availability and loss as affected by method of manure application and animal type.

Year available

Broadcast + >96 hours incorporation

Broadcast + 12-96 hours incorporation

Broadcast + <12 hours incorporation

Injection: Sweep

Injection: Knife

Beef

--

--

--

--

--

1

25% N available/year

45% N available/year

60% N available/year

60% N available/year

50% N available/year

2

25% N available/year

25% N available/year

25% N available/year

25% N available/year

25% N available/year

3

10% N available/year

10% N available/year

10% N available/year

10% N available/year

10% N available/year

Lost

40% N available/year

20% N available/year

5% N available/year

5% N available/year

10% N available/year

Dairy

--

--

--

--

--

1

20% N available/year

40% N available/year

55% N available/year

55% N available/year

50% N available/year

2

25% N available/year

25% N available/year

25% N available/year

25% N available/year

25% N available/year

3

15% N available/year

15% N available/year

10% N available/year

15% N available/year

15% N available/year

Lost

40% N available/year

20% N available/year

10% N available/year

5% N available/year

10% N available/year

Swine

--

--

--

--

--

1

35% N available/year

55% N available/year

75% N available/year

80% N available/year

70% N available/year

2

15% N available/year

15% N available/year

15% N available/year

15% N available/year

15% N available/year

3

0% N available/year

0% N available/year

0% N available/year

0% N available/year

0% N available/year

Lost

50% N available/year

30% N available/year

10% N available/year

5% N available/year

15% N available/year

Poultry

--

--

--

--

--

1

45% N available/year

55% N available/year

70% N available/year

n/a

n/a

2

25% N available/year

25% N available/year

25% N available/year

n/a

n/a

3

0% N available/year

0% N available/year

0% N available/year

n/a

n/a

Lsot

30% N available/year

20% N available/year

5% N available/year

n/a

n/a

In Minnesota, 80% of the P and 90% of the K in animal manures is available the first year. Find the calculations for the first year “Plant Available P” (PAP) and “Plant Available K” (PAK) in Figure 4.